Paper or non-woven fabric of regenerated cellulose fibers and method for producing the same

ABSTRACT

A METHOD IS PROVIDED FOR PRODUCING A PAPER OR NONWOVEN FABRIC OF REGENERATED CELLULOSE FIBERS WHICH PRODUCT IS COMPOSED OF FILM STATE PARTS AND FIBER STATE PARTS. THE METHOD COMPRISES GENERALLY THE STEPS OF: (A) DISPERSING SPUN AND STRETCHED VISCOSE FIBERS COMPRISING HYDROXYMETHYL CELLULOSE XANTHATE (HMCX) IN AN AQUEOUS MEDIUM, (B) FORMING THE DISPERSED FIBERS INTO A WEB BY A WET FORMING METHOD, (C) DEHYDRATING THE WEB TO THE EXTENT THAT THE WATER CONTENT OF THE WEB BECOMES LOWER THAN 700%, (D) SUBJECTING AT LEAST A PORTION OF THE SURFACE OF DEHYDRATED WEB TO PRESSURE THEREBY FUSING AND DECOMPOSING THE HMCX IN THE PRESSED PORTIONS AND SIMULTANEOUSLY BONDING THE FIBERS IN THE PORTIONS TO EACH OTHER, AND (E) SUBJECTING THE PRESSED WEB TO A REGENERATED TREATMENT TO DECOMPOSE THE REMAINING HMCX INTO CELLULOSE.

All}. 27, 1'7. 1 55 K ETAL 3,882,281

v PAPER OR NON-WOVEN FABRIC 0F REGENERATED CELLULOSE FIBERS AND METHOD FOR PRODUCIN THE SHE Filed June 30, 1972 10 Sheets-Sheet 1 Aug. 27, 1974 sus wA ETA L 3,832,281

PAPER OR NON-WOVEN FABRIC 0F REGENERATED CELLULOSE FIBERS AND METHOD FOR PRODUCING THE SAME Filed June 30, 1972 10 Shaw -Shoot 2 Filed June 50, 1972 Aug. 27. 197 ATSUSHI KAWAI ETA 3,332,231

PAPER OR NON'WOVEN FABRIC 0F REGENERATED .CELLULOSB FIBERS AND METHOD FOR PRODUCING THE SAME 10 Shuts-Shoot 3 FUSED AREA/ TOTAL AREA g- 1974 ATSUSHI KAWAI ETAL 3,832,181

PAPER 0R NON-WOVEN FABRIC 0F REGENERATED CELLULOSE FIBERS AND METHOD FOR PRODUCING THE SAME Filed June so, 1972 10 snmssnm Fig. 6

EX PERI MENT 8 EXPERIMENT 7 EXPERIMENT 6 WET TENSILE STRENGTH (kg /inch) EXPERIMENT 5 o '2 4 6 8 IO f2 BONDED FORMALDEHYDE 0.w.f)

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PAPER 0R ON-WOVEN FABRIC 0r REGEIBRATED CELLULOSB.

l'IBmS AND ETHOD FOR PRODUCING I!!! SHE Filed June 30, 1972 10 Shoot-Shut 5 Fig. 8

Aug. 27, 1974 ATSUSHI KAWAI ETA!- 3,83%

PAPER OR NON-WOVEN FABRIC OF REGENERATED CELLULOSE FIBERS AND METHOD FOR PRODUCING IKE SHE Filed June so, 1972 10 sheets-sum s Fig. 9

W- 7', 1974 ATSUSHI KAWAI E-TAL 3,832,281

PAPER OR'NONWOVEN FABRIC OF REGENERATBD GELLULOSB FIBERS AND METHOD FOR PRODUCING THE SAME Filed June so, 1972 10 sheath-sum 7 Fig. /0

Aug. 27, 1'74 'rsusl-u KAWA] ETAL 3,832,281

PAPER 0R NON-WOVEN FABRIC 0F REGENERA'IED CELLULOSI FIBERS AND METHOD FOR PRODUCING THE SHE Filed June 50, 1972 10 Shanta-Shut 8 1974 ATSUSHI KAWAI E AL 3. 31.281

PAPER OR NONWOVEN FABRIC 0F REGENERATED CELLULOSE FIBERS AND METHOD FOR PRODUCING THE SAIE Filed June 30, 1972 10 Shan -Shoot 9 Fig. /2

Aug 27, 1974 'rsusm KAwAl EI'AL 3,582,281

' PAPER OR NON-WOVEN FABRIC or REGENERA'IED cnnmmosa FIBERS AND METHOD FOR rnonucms was SAIE Fi1ed June 5Q, 1972 10 ShOOtlShlOt 1Q United States Patent Office 3,832,281 Patented Aug. 27, 1974 3,832,281 PAPER OR NON-WOVEN FABRIC OF REGENER- ATED CELLULOSE FIBERS AND METHOD FOR PRODUCING THE SAME Atsushi Kawai; Takehiro Katsuyama, Migaku Suzuki,

and Hidenori Ohta, Otake, Japan, assignors to Mitsubishi Rayon Company Limited, Tokyo, Japan Filed June 30, 1972, Ser. No. 267,994 The portion of the term of the patent subsequent to Feb. 27, 1980 has been disclaimed Int. Cl. D21h 1/30 US. Cl. 162-457 C 1 Claim ABSTRACT OF THE DISCLOSURE A method is provided for producing a paper or nonwoven fabric of regenerated cellulose fibers which prodnet is composed of film state parts and fiber state parts. The method comprises generally the steps of:

(a) dispersing spun and stretched viscose fibers comprising hydroxymethyl cellulose Xanthate *(HMCX) in an aqueous medium,

(b) forming the dispersed fibers into a web by a wet forming method,

(c) dehydrating the web to the extent that the water content of the web becomes lower than 700%,

(d) subjecting at least a portion of the surface of dehydrated web to pressure thereby fusing and decomposing the HMCX in the pressed portions and simultaneously bonding the fibers in the portions to each other, and

(e) subjecting the pressed web to a regeneration treatment to decompose the remaining HMCX into cellulose.

This invention relates to papers or non-woven fabrics having an excellent drape and high tensile strength and a method for producing the same. More particularly this invention relates to papers or non-woven fabrics composed of film state parts and fiber state parts. This invention also relates to a method for producing papers or non-woven fabrics by forming the fibers comprising hydroxymethyl cellulose Xanthate in which a fiber making process is connected directly with a web forming process. Such methods are disclosed in US. Pat. 3,320,117 and US. Patent Application 70,421, now US. Pat. 3,718,537, issued Feb. 27, 1973, filed Sept. 8, 1970 which corresponds to Swiss Pat. 512,616.

In US. Pat. 3,320,117 it is disclosed that a viscose is extruded into a low acid content coagulating bath containing zinc sulfate, the resulting incompletely regenerated alkaline fibers comprising less than 20% of residual sodium cellulose xanthate (Cell-O-CS Na) are immersed in water for sufficient time to bring greater than 800% of the swelling degree of the fibers, the swollen fibers are formed into a web and simultaneously bonded each other, and then the web is subjected to after treatment. In this method appropriate swelling (primary swelling) effect of incompletely regenerated fibers comprising sodium cellulose xanthate in neutral or alkaline aqueous solution is utilized to develop necessary self-bonding properties of the fibers in order to produce the web or sheet. And as the web or sheet made of the swollen fibers has a sufficient plasticity in a state of containing more than 1,000% of water, a softness to the touch is imparted to it by pressing it with a net.

In U. S. Patent Application 70,421, now US. Pat. 3,718,- 537, issued Feb. 27, 1973, it is disclosed that a viscose is extruded into an acid coagulating bath containing formaldehyde, the resulting fibers, having a HMCX content in terms of -y-value of greater than 20, are dispersed in a buffer solution, the dispersed fibers are formed into a web, and then the web is subjected to swelling, shrinking, and regeneration. In this method peculiar swelling and/ or dissolving properties of the fibers comprising HMCX are utilized to develop the self-bonding properties for producing a non-woven fabric.

Regardless of the difference in chemical composition of the fibers and the method of development of the selfbonding properties, in both US. Pat. 3,320,117 and Patent Application S.N. 70,421, now US. Pat. 3,718,537, issued Feb. 27, 1973, above described, strengthening of adhesion of the fibers and surface embossing of the web or fabric are performed using the stability and plasticity of the wet web composed of the swollen fibers. Accordingly the adhesion of the fibers and the surface state of the embossed web are reversible so that the web is broken up when it is put into water under shear. According to the prior art, therefore, the setting of the adhered fibers, which are in a stage of surface adhesion between the individual fibers is accomplished by decomposition of cellulose xanthate or HMCX or drying of the Web. Particularly, in case of HMCX containing fiber, decomposition of HMCX in water at a high temperature is essential to set the adhered structure.

Further according to the foregoing prior art, it is necessary to keep the water content of the entire web at a very high level. When the web is pressed to dehydrate and thus to strengthen the fiber adhesion, the web or fabric thus obtained becomes hard and the drape is deteriorated. On the other hand, when the web or fabric is subjected to an embossing treatment to improve the drape, the adhered structure is put into disorder and tensile strength is lowered.

Accordingly, it is most difiicult to produce a non-woven fabric of large weight, high tensile strength and excellent drape according to these prior methods. Therefore, a non-woven fabric having water resistance and draping property comparable to that of woven fabric has been eagerly desired.

One known method to satisfy the desired requirements is to prepare thermoplastic fibers having latent dissolving or fusing properties, to make the length of the fiber in a web as long as possible, to form'strong and non-reversible fiber adhesion in as small a portion as possible in the web by partial heat treatment, and to retain a large portion of the web in the fiber state. Although such partial heat treatment can be applied to a thermoplastic synthetic fiber, for example, Heterofil developed by Imperial Chemical Industries Ltd., but it has been thought to be impossible to use this technique with a cellulose fiber.

It has now been found that the cellulose fiber comprising HMCX has a bonding property at a high temperature similar to that of the thermoplastic synthetic fiber.

According to this invention, a paper or non-woven fabric comprising film state parts and fiber state parts, the specific gravity of the film state parts is at least two times greater than that of the fiber state parts and the area of the film state parts is 5 to 40% of total surface area of the paper or non-woven fabric, are produced by (a) dispersing spun and stretched viscose fibers comprising HMCX in aqueous medium having a pH of lower than 6.0 at a temperature of lower than 30 C.,

(b) forming the dispersed fibers into a web by a wet forming method,

. .3v a (c) dehydrating the web to the extent that water content of the web becomes lower than 700%, the fibers after dehydration being characterized by: j

(1) HMCX content in terms of 'y-value of greater than 30, (2) a decomposition degree of less than 75%, and (3) a process swelling degree of lower than 250%, (d) subjecting at least a portion of the surface of the dehydrated Web to a pressure of greater than 2 kg./ cm. at a temperature of 90 to 180 C., thereby fusing and decomposing HMCX in the pressed portion of the fibers and simultaneously bonding the fibers in said portion to each other, and (e) subjecting the pressed web to a regeneration treatment to decompose the remaining HMCX into cellulose.

FIG. 1 illustrates diagrammatically one form of apparatus suitable for the web formation in this invention,

FIG. 2 is a schematic, cross-sectional view of the fiber dispersing baths shown in FIG. 1,

FIG. 3 is a schematic, plane view of the fiber dispersing baths shown in FIG. 1,

FIGS. 4 and 5 illustrate schematically two forms of apparatus suitable for carrying out heat pressing in this invention,

FIG. 6 shows the relationship between bonded formaldehyde content and wet tensile strength of the web,

'FIG. 7 shows the relationship between fused area of the web and decomposition of formaldehyde,

FIGS. 8 to 11 are the scanning type electron microscopic photographs of the web,

FIG. 12 is scanning type electron microscopic photographs of the heat embossed part of the Web,

FIG. 13 is a microscopic view, magnification of which is 50, of a film state part of the Web of this invention.

To aid in describing the web formation in this invention, reference will now be made to FIGS. 1 to 3. In FIGS. 1 to 3, a bundle of filaments 1, which is produced by the spinning and stretching, is cut with a cutter 2 into short fibers or chips. The chips are supplied to a hopper 3. The hopper has a jacket 26 the inner wall of which is provided with a large number of small holes 27.

Water is supplied to the jacket 26 through a pipe 4, and flows out from the small holes, serving to prevent the chips from adhering to the inner wall. The chips fed in the first dispersing bath 5 through the hopper 3 are dispersed with water streams supplied through pipes 6 and 7. This dispersion is supplied to the second dispersing bath 9 in which the dispersion of the chips is completed with Water streams supplied through pipes and 11. 28 and 29 are small holes from which the water stream is discharged. The dispersed chips and water are further transferred to a wire drum 13 through a stream rectifying zone 12. The water supplied to the wire drum is drawn out by a suction pump 15 through a pipe 14 and back to a storage tank 8. A wet web formed from the chips on the wire drum is taken oil with a wet felt 16 and then with a top felt 17.

Referring to FIGS. 4 and 5, 18 is a heated embossing roll, 19 and 21 are rubber rolls, is a heated roll, and 22 is a plastic net.

The starting material for use in this invention is filaments or fibers comprising HMCX, which is the reaction product of formaldehyde and cellulose xanthate. To obtain this material, various methods may be employed. For example, the filaments may be produced by extruding a viscose to which formaldehyde is added or by adding formaldehyde to a coagulating bath or by treating spun filaments comprising cellulose xanthate with an aqueous solution of formaldehyde.

Viscose used in this invention preferably contains 2 to 8% total alkali. The polymerization degree of cellulose in the viscose is preferably lower than 700. The viscose during spinning should have a salt point of at least 12, preferably of 15 to 24. When formaldehyde is added to viscose, the amount of the former is preferably 0.5 to 2% based on the weight of the viscose.

Excess amounts of low boiling point solvents such as carbon disulfide, methanol, acetone, etc. or materials capable of being decomposed in an acidic state to generate a gas such as ammonium carbonate, sodium bicarbonate etc. may be added to viscose to provide a foaming effect and to occlude the gas in the subsequently formed web. Furthermore, phosphorus containing compounds or halogen containing compounds which provide a fiameproofing effect may also be incorporated into the viscose.

The coagulating bath contains 20 to 250 g./l. sodium sulfate, less than 0.1 g./l. or no zinc sulfate and 20 to 120 g./l. sulfuric acid. In connection with development of crimps, the especially preferable range of concentration of sulfuric acid is shown by the following equation.

Minimum concentration of sulfuric acid (g./l.) =3A +8 Maximum concentration of sulfuric acid (g./l.)=8A+l6 Wherein A is the total alkali concentration (percent) in the viscose.

When formaldehyde is not added to the viscose, the coagulating bath contains preferably 4 to 20 g./l. formaldehyde. When formaldehyde is added to the viscose, the formaldehyde concentration in the coagulating bath may be 0.5 to 6 g./l. The temperature of the coagulating bath is below 35 C., desirably 10 to 25 C.

Filaments comprising HMCX may be obtained by extruding having a 'y-value of greater than 70 into a coagulating bath containing 14 to 50 g./l. sulfuric acid, 20 to 250 g./l. sodium sulfate and less than 1 g./l. or no zinc sulfate at a temperature of lower than 35 C. and treating thus formed filaments with an aqueous solution containing 15 to 70 g./l. formaldehyde without adding formaldehyde to the viscous or the coagulating bath.

In all the above cases, the coagulating bath or the viscose may contain various surface active agents.

The filaments thus formed are preferably stretched in an acidic aqueous solution, heated inert non-aqueous liquid or saturated steam, at a temperature of no lower than 40 C. to give the filaments excellent fiber structure.

Utilizing the principle disclosed in U.S. Pat. 3,419,652, namely, controlling the stretch ratio, it is possible to produce the filaments of a latent crimping property as well as a latent adhesive property. The filaments so stretched result in a web in which crimps can be developed by heat treatment.

Stretching conditions are not particularly critical for the preparation of fibers used in the process of this invention. However, a preferable stretch ratio is 30% to 70% of the maximum stretch ratio.

The spun and stretched fibers, which are used in the process of this invention, should contain a sufficient amount of HMCX so that the resulting web is effectively fused and bonded when subjected to the heat pressing treatment. In this invention it is also necessary to control the swelling degree of the fibers so that the fibers of the resulting web are bonded to each other only in the fused portions.

The content of HMCX in the fiber (referred to hereinafter as HMCX content for brevity) can be represented conveniently by the content of carbon disulfide or formaldehyde bonded with a glucose chain. In general the content of bonded carbon disulfide in sodium cellulose xanthate (Cell-0-CH Na) is expressed by value, which is defined as one hundred times the molar proportion of bonded carbon disulfide to the glucose unit (C H O This indication can be similarly employed for the indication of the HMCX content.

In this connection, when one mole of formaldehyde is combined with one glucose unit, the content of bonded formaldehyde is aproximately 18.5%, which content corresponds to if expressed in terms of -value. In

5 the actual measurement, the HMCX contact determined in terms of 'y-value is usually higher than that determined in terms of the content of bonded formaldehyde only to a slight degree, i.e. approximately 5%.

The HMCX containing fiber used in this invention is further characterized by decomposition degree.

The decomposition degree is a value represented by the ratio of the 'y-value when the decomposition degree of viscose just before spinning is taken as and that of completely decomposed cellulose xanthate is taken as 100%. Thus, for example, if the 'y-value of the viscose is 80 and that of the fiber dispersed in a dispersing bath after spinning and stretching is 32, the decomposition degree of the fiber is calculated as follows:

In order that the resulting web is effectively fused and bonded when subjected to the pressing treatments the spun and stretched fiber preferably has a HMCX content in terms of -value of greater than 30 most preferably greater than 40, in terms of the content of a bonded formaldehyde content of greater than most preferably greater than 6.5% and a decomposition degree of less than 75%, most preferably less than 70%. When the fiber has a 'y-value of less than 30, a content of bonded formaldehyde of less than 5% and a decomposition degree of more than 75 it does not provide a web which is effectively fused and bonded.

The HMCX containing fiber is stable in acidic conditions, particularly of a pH of no more than 4.5, but decomposes and rapidly swells or dissolves under neutral and alkaline conditions. Therefore, the pH of the dis persing medium should be maintained lower than 6.0, preferably lower than 5.0.

The swelling degree which the HMCX containing fiber exhibits in aqueous mediums in each step of this inventin is herein referred to as process swelling degree. The procedure of determining the process swelling degree will be set forth later.

In this invention the HMCX containing fiber should not swell to an extent that it exhibits a process swelling degree of more than 250%. The swelling degree is preferably maintained as low as possible throughout the process steps of this invention.

In addition to pH, swelling or dissolution of the HMCX containing fiber largely depends upon temperature and time, and the composition of the solution as disclosed in US. Patent Application Ser. No. 70,421, now US. Pat. 3,718,537, issued Feb. 27, 1973. That is, the fiber is not readily swollen at a low temperature within a short period, but rapidly swollen or dissolved at a high temperature. Further, the HMCX rapidly decomposes at a temperature of higher than approximately 60 C.

The spun and stretched fiber employed in this invention may be either in the form of continuous filaments or short fibers. In general the latter is preferred.

In the preferred embodiment, the spun and stretched filaments containing HMCX are first fed to a cutter where the filaments are cut into short fibers having a length of more than 5 mm., preferably from mm. to 30 mm. The fibers so cut are then introduced into and dispersed in the dispersing bath. The introduction and dispersion is preferably carried out in as short a time as possible and in a continuous manner. For this object, it is preferable to employ the first and second dispersing baths as shown in FIGS. 1 to 3.

The time from when the filaments are cut until the short fibers are put into the dispersing bath is preferably within 5 minutes, and most preferably within 3 minutes. In the case where the spun and stretched filaments are preserved for a period longer than the above range, the filaments should be maintained under conditions such that the filaments have a moisture percentage pH about 4.5 Cell-O-CSr-CH2OH (HMCX) Cell-O-CSr +CH2OH pH about 4.5

Therefore, HMCX is stable under acidic conditions or in the presence of OH 0, but becomes unstable with an increase of pH. In this connection, when a fiber containing a large amount of HMCX is placed in a buffer solution at a pH of 7.0 while being stirred, the fiber dissolves within a few minutes or more.

The decomposition of HMCX accelerates with an increase of temperature. Therefore, the aqueous dispersion of the HMCX containing fibers should be maintained at a low temperature, i.e. lower than 30 C. preferably lower than 25 C.

Likewise, the residence time in the aqueous dispersing medium, i.e. the period from the time the fibers are put into the dispersing medium until a web is formed is preferably shortened as much as possible. The period is preferably within 10 minutes, most preferably within 8 minutes.

For these reasons, in this invention a continuous dispersion system is preferred such as, for example, shown in FIG. 1.

As additives for the dispersing medium, dispersing agents such as polyethylene oxide, carboxymethylcellulose, sodium polyacrylate, and polyacrylic amide and various latexes may be used.

The concentration of fibers in the dispersing medium is preferably 0.01 to 1%. Various paper making machines may be used as apparatus for forming a web from the fibers dispersed in the medium. For example, a Fourdrinier paper making machine or a cylinder type paper making machine may be used.

The web so formed is immediately dehydrated to the extent that the process moisture percentage of the web is preferably reduced lower than 700%, most preferably lower than 600%. The process moisture percentage is defined hereinafter. For optimum results the lowest possible water content is preferable for the following reasons:

(1) It is advantageous to leave little or no space between the fibers, i.e. to make the individual fibers as close to each other as possible.

(2) Unnecessary water should be removed from the web, so that when the dehydrated web is subjected to the heat pressing, the undesirable influence of water conducted heat on the non-pressed portions can be avoided.

(3) When the dehydrated web is subjected to the heat pressing treatment, the heat loss inevitably caused by heating the remaining water contained in the web should be minimized to improve heat efficiency.

As set forth above, the web is dehydrated to the extent that the process moisture percentage reaches lower than 700%. It is noted however that when the dehydrated web is subjected to the heat pressing treatment to fuse HMCX in the pressed portions, the remaining water exercises a plasticizing effect on the web and, therefore, a process moisture percentage of at least should preferably be maintained.

The dehydrating may be carried out in a known manner such as, for example, by vacuum hydration or a press hydration process. It should be noted, however, that before dehydration of the fibers there is no substantial adhesion between the individual fibers of the web and thus the web has too low a tenacity to support itself. There fore, it is usually necessary to use a suitable support for the web, such as a felt, in order to perform the dehydration.

As well as the process moisture percentage, the process swelling degree of the fiber should preferably be maintained as low as possible. The process swelling degree is maintained at lower than 250%, preferably lower than 200%.

As set forth above, it is an important feature of this invention that the characteristics of the starting fiber, i.e. the HMCX containing fiber as spun and stretched, are maintained substantially constant to the extent practicable until the web is subjected to the heat pressing treatment. Accordingly, the fibers should exhibit a decomposition degree of less than 75% and a HMCX content in terms of 'y-value of greater than 30 immediately before the web is subjected to the pressing treatment. Content of bonded formaldehyde in the fiber is preferably greater than based on the weight of fiber before the heat pressing.

Then, the web thus dehydrated is subjected to pressing in such a manner that at least a portion of the surface of the dehydrated web is pressed at a pressure of greater than 2 kg./cm. and a temperature of 90 to 180 C.; thereby fusing and decomposing HMCX in the pressed portion of the fibers and simultaneously bonding the fibers in said portions to each other. The expression kg./cm. refers to the Weight in kg. applied to the web along the length (in cm.) of the pressing roll.

When HMCX is heated at temperatures of higher than approximately 60 C., thermal decomposition occurs as follows:

The thermal decomposition reaction rapidly proceeds at a temperature of higher than approximately 90 C. When HMCX is decomposed in such a manner, the fibers containing HMCX in the amount in terms of 'y-value of greater than 30 exhibit fluidity and rapidly change in volume and simultaneously, the HMCX is converted into cellulose. To say this more exactly, when a web comprising randomly laminated fibers containing a large amount of HMCX is subjected to pressing treatment, in such a manner that at least a portion of the surface of the web is exposed to sufficient heat and pressure, the fibers are melted and flow into each other, leading to the self-diffusion of the constituent molecule only in the pressed portions due to the thermal motion of segment, whereby a web structure completely bonded only in the pressed portions is obtained. Simultaneously, the HMCX is thermally decomposed and converted into cellulose. Thus, a quite irreversible structure is formed. Accordingly, in the pressed portions the fiber state substantially disappears, forming a film state like cellophane. Examples of these states are shown in FIGS. 8 through 12.

Such heat pressing accompanied by the thermal decomposition of HMCX is characterized by, not a mere interfacial interaction of the fibers, but a stereometric interaction, i.e. the structure is a completely cohered structure. The structure is, therefore, can not be separated into laminae. At first sight this latter phenomenon is completely similar to that observed when thermoplastic materials such as polyvinyl chloride fibers are bonded by high frequency induction heating. However, the phenomenon of this invention is fundamentally different from that of poly- -vinyl chloride fibers. That is, the joined surfaces of polyvinyl chloride fibers are thermoplastic. In contrast, the joined surfaces of this invention are not thermoplastic, and the structure is completely irreversible. This is because HMCX is decomposed to cellulose by the heat pressing. This irreversibility is attained simultaneously with the fusing and bonding.

The above phenomenon appears due to the facts that, first, HMCX fuses and decomposes when heated and secondly, the HMCX containing fiber has an amorphous l) HMCX content (2) Heating time (3) Heating temperature (4) Pressure The configuration of the fused and bonded portion of the web varies greatly depending upon the HMCX content, as seen from the comparison of FIGS. 8 to 11 when studied in conjunction with Example 1.

The heating temperature is from to 180 C., preferably to C. When the temperature is lower than 90 C., the fiber is not instantly fused. In contrast, when it is higher than C., the decomposition of cellulose inevitably occurs. Known heating means may be employed such as, for example, a heated roller heated by steam, heat transfer medium or an electrical heater, a high frequency induction heater and in infrared heater. Among these heating systems, an inner heated roller heated by steam is preferable because it has a heat capacity sulficient for the heat treatment of the wet web.

A suitable temperature can be selected within the range set forth above, depending upon the thickness, moisture percentage and travelling speed of the web; the HMCX content and the ratio of the area to be fused to the total area of the web, and the projections on the roller surface (when an embossing roller is employed).

The pressure applied is greater than 2 kg./cm., preferably from 3 kg./cm. to 50 kg./cm. When the pressure is smaller than 2 kg./cm., heat does not penetrate into the web even though the heating temperature is high, and consequently, only the surface layer of the web is fused. In contrast, when the pressure is too high, the web may crack in the pressed portion.

The fusing of the web is accompanied by the decomposition of HMCX and the fused portion changes to a film state. That is, when the HMCX containing fiber is subjected to the heat pressing treatment, the HMCX decomposes thereby to evolve gaseous formaldehyde. The amount of HMCX decomposed depends upon the fused area of the web as understood from FIG. 7. With an increase of the fused area, the strength of the web increases but the web becomes hardened and film-like. Therefore, in order to produce non-woven fabric of a feeling soft to the hand it is preferable that the ratio of the fused area to the total area of the web is kept as low as possible as long as the strength of the web is not significantly reduced. In this invention, the fused area (film state parts) is preferably 5 to 40% of total surface area of the web. It is, consequently, advantageous that the web is subjected to a spotlike heat pressing over its entire surface. Two preferable embodiments of the pressing rollers are shown in FIGS. 4 and 5. In FIG. 4, a web is passed between an embossing roller 18 internally heated by steam and a bottom roller 19. In the embodiment shown in FIG. 5, a net 22 made of, for example, plastic material is employed instead of the embossing roller 18.

Further, it is preferable during the application of heat and pressure to restrict clearly the areas to be fused from those which are not fused, i.e. distinguish the film state parts from the fiber state parts, as definitely as possible thereby to minimize the non-fused portions being damaged by the heat. Accordingly, some considerations should be taken, for example, of the height of projections of the embossing roller shown in FIG. 4 and the thickness and the material of the net shown in FIG. 5. In this invention, the web may be subjected to the heat pressing treatment under such conditions that small holes are formed through the web at the heated portions. 9

The non-woven fabrics thus manufactured consists 0 two kind of parts, i.e. non-woven fibrous, bulky parts, having a low apparent specific gravity, and transparent film state parts, having a high apparent specific gravity. The apparent specific gravities of the two portions are approximately 0.02 to 0.3 and approximately 0.7 to 1.4, respectively. In general the apparent specific gravity of the latter is greater than twice that of the former.

Various non-woven fabrics of different appearance can be manufactured by modifying the pressing conditions. Using a roll at very high temperature, but pressed with somewhat reduced pressure, only the one side of the web is fused and becomes transparent whereby a peculiar web structure is obtained. The appearance of the structure is shown in scanning type electron microscopic photographs in FIG. 12.

When a web is pressed with a heated embossing roller with sharp-pointed projections at a high temperature, the fused portions of web are made to flow and remarkably shrink due to the setting of structure caused by the decomposition of HMCX. Consequently, a. small hole is made at the center of each portion. In FIG. 13, the peripheral portion 23 of each hole 24 has the appearance of transparent film or the state such that the fibers are fused and bonded to each other. In FIG. 13, 25 is a fiber state part.

Although the bonded structure manufactured by the process of this invention is very stable as set forth above, the film-like part tends to become brittle. This tendency offers problems, particularly when a web is treated at a high temperature and a high pressure. This tendency results from the fact that the fine structure of the initial viscose fiber collapses and the orientation of molecule chain is disordered from causes such as the instantaneous cubic expansion, the cubic reduction caused by the setting of structure due to the decomposition of HMCX and the generation of voids, at the time of heat fusing. The above tendencies will be seen from Table 4. It is noted, however, that when a web is pressed spotlike, the resulting web has an improved tensile strength even though the heating temperature is rather high.

The undesirable hardening of the fused and bonded area having the appearance of film can be avoided or minimized by blending infusable fibers, which do not fuse at the heating conditions, with the HMCX containing fiber. The effect of blend of the fiber will be seen from Table 4.

The ratio of the infusable fiber to the HMCX containing fiber is preferably below 60/40, by weight. When the ratio exceeds the limit, the tensile strength of web is reduced. Any infusable fibers can be employed provided that they do not fuse when passed between heated rollers at a temperature of 90 to 180 C. in a wet condition. These fibers include, for example, pulp, viscose rayon, acrylic fiber, polyester fiber, polyamide fiber, acetate fiber and the like.

Then, the web, at least a portion of which has been thus pressed, is subjected to a regeneration treatment to decompose the remaining HMCX into cellulose. In general the regeneration is carried out by treating the web with an aqueous acidic solution at a temperature of higher than 50 C.

In the case where shrinking or crimping of the fiber is performed simultaneously with the regeneration, by utilizing the shrinking or crimping property of the remaining HMCX in the non-fused areas, it is preferable that the web is treated by the following two steps. First, with an aqueous acidic solution at a temperature of approximately 50 to 70 C. and then, with an aqueous acidic solution at a temperature of approximately 80 to 90 C. These two steps result in the development of uniform srinkage or crimp. In this case, the fibers have preferably a HMCX content in terms or 'y-value of greater than 50%, a decompostion of less than 63% and a process swelling degree of less than 200%.

The regenerated cellulose fibers in web form are then scoured and dried. Scouting includes a bleaching step, a neutralizing step, a washing step and other treating steps which are conventional in the art. The scouring step may be followed by treatment with softening agents, fireproofing agents, sanitary finishing treatment, dyeing and various latex treatments.

The non-woven fabric or paper manufactured by using a suitable embossing roller of various patterns or configurations can be directly placed on the market as various goods. In connection with the weight per unit area, various products having a weight per square meter of 10 g. to 200 g. can be obtained. The process of this invention is, however, particularly suitable for the production of weighty products having a weight per square meter of more than 20 g.

The paper or non-woven fibrous product prepared by the process of this invention resembles woven fabrics in physical properties, bulkiness, drape and feeling. It has a superiority in water resistance and durability under repeated washing over other non-woven cellulose fabrics. The paper or non-woven fibrous product has various uses. For example, it is useful as throw-away type goods such as sanitary goods (tampon, pad), sheets, tablecloth, baby wear and diapers because it is mainly comprised of cellulose and hence the waste disposal is simple. It also has a wide range of uses such as wall materials, auxiliary material for civil engineering and construction industry, curtains.

The following examples are given to illustrate this invention without limiting its scope. Throughout the examples, were measured salt point, 'y-value, bonded formaldehyde, process swelling degree, and process moisture percentage as follows:

(i) SALT POINT Aqueous sodium chloride solutions of from 10.0 to 25% concentration were prepared and kept at 20 C. 20 cc. of each solution was added to test tubes. About 0.1 g. of the viscose was then dropped into the each tube and each of the solutions were vigorously stirred. The solution concentrations where the salting out began after about one minute from the end of vigorous stirring was taken as salt point.

(ii) 7-VALUE Sample viscose or fibers of about 2 g. in terms of cellulose was dissolved in 200 cc. of 4% aqueous sodium hydroxide solution at 5 C. and the solution was stored in a freezer of a refrigerator.

Removing by-products of carbon disulfied by treating the sample with OH type ion exchange resin, bonded carbond disulfied was estimated by iodometry.

'y-value was calculated from the titer and cellulose content in the sample.

(iii) BONDED FORMALDEHYDE There was sampled about 2.0 g. in terms of cellulose of stretched filaments or wet web. The sample was washed with 200 cc. of 0.2 g./l. aqueous sulfuric acid and then dehydrated. The dehydrated sample was put in a conical flask containing cc. of 10 g./l. aqueous sulfuric acid solution and then the solution was boiled at 100 C. for 20 minutes under reflux to decompose and dissolve out the formaldehyde. Letting it cool, the solution was separated from the fiber by filtration with a glass filter. The filtrate was diluted to 250 cc. in a measuring flask. Sampling 25 cc., the diluted solution was titrated by hydroxylamine hydrochloride method to determine the formaldehyde content.

On the other side, the filtered fibers were dried to the bone dry condition. Bonded formaldehyde was calculated from the following equation:

The term Process swelling degree means the swelling degree of the fiber at each step.

1 1 1 2 About 1.0 g. in terms of cellulose of the stretched filamew-i ments or wet web was sampled, immediately dehydrated Eng; NW] by a centrifugal hydroextractor at 3,000 rpm. for 3 min- 5 g g utes, and then weighed (A). 8

The dehydrated fiber sample was further dried to a bone 5 A p 0M3 dry condition and then weighed (B). g The process swelling degree was calculated from the following equation: as

Process swelling degree (percent)= 100 10 is E? '3 3 c: H

(v) PROCESS MOISTURE PERCENTAGE 2 fi The term process moisture percentage means the QQflfff moisture percentage of the fiber at each step. g 55% About 2 g. in terms of cellulose of the stretched filao ments or wet web was sampled and immediately weighed 3 (C)' E wa The sample was further dried to a bone dry condition and weighed (D). The process moisture percentage was calculated from the following equation: .5 as a Process moisture percentage (percent)= X 100 3 E 3 D a g a: "at; ease Example 1 (Effect of the concentration of formaldehyde 2 fig added to a coagulating bath) 51.3 A viscose containing 8.0% cellulose having a polymwe N erization degree of 400 and 5.5% total alkali, and hav- 515E ing a viscosity of 133 seconds, a salt point of 23.0, and a 'y-value of 93 was extruded into a coagulating bath con- 5 taining 32 g./l. sulfuric acid, 80 g./l. sodium sulfate, and h I coon 0 to 12 g./l. formaldehyde at 20 C. to form filaments. gag EQEQ Filaments thus formed were withdrawn from the coagulatg I ing bath and then stretched at a stretch ratio of 50% of 35 the maximum stretch ratio in a second bath containing 3 .-i g m O we g./l. sulfuric acid at 60 c. g 5 egg 22321 HMCX content ('y-value and amount of bonded formto 55% S aldehyde), process moisture percentage, and process swell- 40 a E- ing degree were measured and the results are shown in a up Hem Table 1.. g 5 228% Directly after stretching, the stretched filaments were 5; egg continuously supplied to a cutter at a speed of 13 m./ min. 5 and cut to chips of 15 m./m. long. The speed of fiber production was 13 m./min. g The chips were put into water containing 10 p.p.m. of 5 P.E.O.-PD (polyethylene oxide having a molecular weight 2% 1 00 of 3,600,000 produced by Sietetsu Kagaku K.K., Japan) M and having a pH of 3.5 at 18 C., dispersed in the water Mei-4H for 3 minutes using an apparatus as shown in FIGS. 2 and a 3, and then formed into a web using a cylinder type paper making machine having a cylinder wire drum of 70 cm. m? 31,060 in width at a speed of 3 m./rnin. In this example it took w 8431 5 222 about 30 seconds from the finish of the stretching until the 5+3; finish of the cutting and about 3 minutes from the time Q 1 8 the chips were put in the water until the web was formed. AA The web was immediately dehydrated with a Nush suc- 5 g tion pump (Liquid-piston type pump) and press rolls hav- +1 1% Egg ing a polytetrafluorethylene coating. Process moisture perg g 8 centage, process swelling degree, and HMCX content (7- E, f, 0A oeecnoo value and bonded formaldehyde) of the web were mease E EEFI ured and the results are shown Table 1. E .E @5 (When the coagulating bath containing no formaldehyde was used, measurement error was large due to insufiicient OUA e; dissolution of the fiber in aqueous alkaline solution.) 5 'E'gf' The dehydrated web was immediately passed through 5 a pair of rolls as shown in FIG. 4 under a pressure of 5 m kg./cm. at a speed of 3 m./min. to fuse a portion of the 5 i i 1 surface of the web spot-like and simultaneously to fix the i E i i wbe structure. In FIG. 3 (18) is a heated embossing roll i i i 5 and 19 is a rubber roll. In this example the surface of z E i i 5 the embossing roll was at 120 C. g i i i i The embossed 'web was subjected to a shrinking treati i E ment in water containing 0.5 g./l. sulfuric acid and 5 g./l. 3 i E E sodium sulfate at 65 C. for 2 minutes and then subjected i-i'o'm'e .13. to a regeneration treatment in acidic aqueous solution containing 1 g./l. sulfuric acid at 80 C. to completely decompose the remaining HMCX into cellulose.

The web was subjected to washing with water, bleaching with sodium hypochlorite, neutralizing with sulfuric acid and washing with water. It was then dried by a Short loop type dryer using heated air.

Properties of the web thus obtained are shown in Table 2.

seconds, a salt point of 22.5 and a 'y-value of 90 was extruded into a coagulating bath containing 35 g./l. sulfuric acid, 120 g./l. sodium sulfate, and 12 g./l. formaldehyde at 25 C. to form filaments. Filaments thus formed were withdrawn from the coagulating bath and then stretched 170% of the original length in a second bath containing g./l. sulfuric acid at 55 C. to form a bundle of 60,000 filaments, filamentary denier of which was 3.

TABLE 2 Thickness of the Apparents ecifle web (m./m.) gravity (g. cm!) Tensile Not State Not strength Elongation heat Heat otheat heat Heat (kg/inch) (percent) Bending Experi- Weight pressed pressed pressed pressed pressed resistance ment No. (g./m. portion portion portion portion portion Dry Wet Dry Wet (cm.) Figure FIGS. 8 to 11 are the scanning type electron microscopic photographs of the heat pressed portion of the webs. Among those figures, each (A) shows the surface condition at a magnification of 300 and each (B) shows the cross-sectional condition at a magnification of 1,000.

In the case of Experiment No. 1 (FIG. 8), the bonding between fibers was so weak that continuous production o the web was impossible. In the case of Experiment No. 2 (FIG. 9), continuous production of the web was possible, but the web obtained had a low tensile strength and paper like feeling to the touch.

In the case of Experiments Nos. 3 and 4 (FIGS. 10 and 11) the web obtained had a high tensile strength and fabric like hand feeling to the touch.

Example 2 (Effect of fused area) Four kinds of dehydrated webs were prepared using the same conditions as that of Experiment No. 4 in Example 1. The webs were subjected to heat pressing treatment under the conditions as shown in Table 3.

TABLE 3 Web Surface pass- Fused Projection tempera- Presing area] of pressture of sure speed total Experling roll pressing (kg./ (m./ Fusing areaXlOO ment No. surface r011( 0.) cm.) min.) pattern (percent) 5 0 120 5 3 Spot 13 fusing 120 5 do 18.9 120 5 3 Entire 100 fusing Tensile strength of the webs thus obtained are shown in FIG. 6.

Example 3 (Eifect of fused area) A viscose containing 7.5% collulose of polymerization of 300 and 4.5% total alkali, and having a viscosity of 80 HMCX content of the stretched filaments was 12.4% in terms of bonded formaldehyde and 72 in terms of 'y-value. Thus the decomposition degree was 20%.

The process swelling degree was 161%.

The stretched filaments (a bundle of filaments) were supplied to a cutter at a speed of 15 m./min. and cut to chips of 20 m./m. long.

The chips were put into water containing 15 p.p.m. of P.E.O.-PD and having a pH of 4.5 at 25 C. and dispersed in the water using an apparatus as shown in FIGS. 2 and 3 and then formed into a web using a cylinder type paper making machine having a cylinder wire drum of 50 cm. in width at a speed of 3 m./min. In this example it took about 40 seconds from the finish of the stretching until the finish of the cutting and 4 minutes on average from the time the chips were put into the water until the web was formed.

Resulting web had a weight of g./m. and a width of 50 cm.

The web thus formed was immediately dehydrated in the same manner as in Example 1 to a moisture percentage of 540. The web after dehydration had a process swelling degree of 146%, a bonded formaldehyde of 11.6% o.w.f., a -value of 65, and a decomposition degree of 28%.

The dehydrated web was immediately subjected to a heat pressing treatment. Conditions of the pressing treatment were as follows:

Surface temperature of the embossing roll: 0.

Pressure: 10 kg./cm.

Passing speed of the web: 5 m./min.

The ratio of fused area to total surface area of the web:

A bonded formaldehyde of the web before heat pressing being taken as A and a bonded formaldehyde of the sheet after heat pressing as B, the relationship of the B/A and the ratio of Fused area/Total area is shown in FIG. 7. For instance when 80% of the total surface area was fused, the amount of the bonded formaldehyde was reduced from 11.6% to 4.1% in other words 65% of the bonded formaldehyde was decomposed at the heat pressing step.

Example 4 (Effect of heat pressing temperature) A viscose containing 6.5% cellulose (of polymerization degree of 600) and 4% total alkali and having a viscosity of seconds, a salt point of 24.0, and a 'y-value of 95 was extruded in a coagulating bath containing 30 'g./l. sulfuric acid, 80 g./l. sodium sulfate, and 10 g./l. formaldehyde at C. to form filaments. Filaments thus fordehyde at 20 to form filaments. Filaments thus formed Table 4 also shows the properties of the Web thus obtained at 20 C. under wet conditions.

1 Cell=Fiber comprising HMCX. 1 AN =Acrylic fiber.

were withdrawn from the coagulating bath and then stretched 180% of original length in a saturated steam of 102 C. for 2 seconds to form a bundle of 80,000 filaments, 2

filamentary denier of which was 1.5. Maximum stretch was 350%.

HMCX content of the stretched filaments was 11.8% in terms of bonded formaldehyde and 68 in terms of -value. Thus the decomposition degree was 28.5%.

The stretched filaments (a bundle of filaments) were supplied to a cutter at a speed of 13 m./min. and cut to chips of 15 m./m. long.

The chips were put into water having a pH of 4.0 at 28 C. to give a 0.1%v dispersion, dispersed in the water and then formed into a web using a cylinder paper making machine having a cylinder wire drum of 50 cm. in width at a speed of 3 m./min. In this example it took about 3 minutes from the time the chips were put in the water until the web was formed.

The formed web was dehydrated to a moisture percentage of 400.

The web after dehydration had a process swelling degree of 143%, a bonded formaldehyde of 10.2% o.w.f., a value of 57, and a decomposition degree of 40%.

The hydrated web was subjected to a spot-like heat pressing treatment under conditions as follows:

Surface temperature of the embossing roll: 122 C., 146

Pressure: 15 kg./crn.

Passing speed of the sheet: 3 m./ min.

The ratio of fused area to total surface area of the sheet:

The heat pressed web was subjected to a treatment with an aqueous bath containing 1 g./l. sulfuric acid at 60 C. for 2 minutes and then subjected to washing, bleaching, neutralizing, washing, and drying according to conventional methods. Table 4 shows the properties of the web thus obtained at 20 C. wet condition.

Example 5 (Web forming form mixed fibers) Example 4 was repeated except that a bundle of 32,- 000 acrylic filament, filamentary denier of which was 3 (produced by Mitsubishi Rayon Company, Ltd., Japan) was supplied to the cutter together With the stretched filaments in Example 4 in piles to form mixed chips.

What is claimed is:

1. A paper or non-woven fabric of regenerated cellu- I (b) forming the dispersed fibers into a Web by a Wet forming method,

(c) dehydrating the web to the extent that the Water content of the Web becomes lower than 700%, said fifibers after dehydration being characterized by:

(1) a hydroxymethyl cellulose xanthate content in terms of 'y-value of greater than 30',

(2) a decomposition degree of less than and (3) a process swelling degree of lower than 250%,

(d) subjecting at least a portion of the surface of dehydrated web to a pressure of greater than 2 kg./ cm. at a temperature of to C., to produce film state parts covering about 5 to 40% of said surface, the treatment fusing and decomposing the hydroxymethyl cellulose xanthate in the pressed por tions of the fibers and simultaneously bonding the fibers in said portions to each other in the film state, and

(e) subjecting the pressed web to a regeneration treatment to decompose the remaining hydroxymethyl celluose xanthate into cellulose.

References Cited UNITED STATES PATENTS S. LEON BASHOR E, Primary Examiner P. *CHIN, Assistant Examiner US. Cl. X.R. 

